Sewing machine control device

ABSTRACT

This invention relates to a sewing machine control device which precisely and effectively stops a sewing machine at the termination point of a seam. The sewing machine control device comprises operation means (LSW) for producing an actuation signal or a stop signal, needle position detector means (NP), workpiece detector means (5, WS) operatively connected to said operation means and an electrical circuit operatively connected to said workpiece detector means. When the operation means drives or stops the sewing machine and the workpiece detector means detects the trailing end edge of a workpiece, the electrical circuit automatically stops the sewing machine.

TECHNICAL FIELD

This invention relates to a sewing machine control device and, moreparticularly, to improvements in a sewing machine control device wherebya sewing machine can be precisely and effectively stopped at thetermination point of a seam.

BACKGROUND TECHNOLOGY

In sewing machines generally, it has been known that at the sewingtermination point of one of a plurality of continuous sewn portions of aworkpiece or at the termination point of the sewing operation for allthe sewn portions, the sewing machine must be precisely stopped so thatthe seam or seams will not deviate from the end of the workpiece.

Hithertofore, a variety of methods for stopping sewing machines in sucha manner have been attempted.

According to the first method, when a seam is formed to finish at aposition adjacent to an end edge of a workpiece where the sewingoperation is scheduled to terminate, the operator reduces the forceapplied to the pedal so that the sewing machine is driven at a lowspeed, stops the machine when the seam reaches the predetermined sewingtermination point and then depresses the pedal again to effect threadcutting. However, this method requires that the operator controls thepedal with great care. According to the second method, a workpiecedetector means utilizing light is disposed upstream of the sewing zonein the sewing machine in the workpiece feed direction and the sewingmachine stops automatically as the trailing end edge of a workpiecepasses by the workpiece detector means independently of the pedalcontrol. However, this method involves the drawback that when a seam isformed along an end edge of a workpiece having a complicatedconfiguration such as a wave or concavo-convex shape, for example, theworkpiece end edge tended to deviate at concavo-convex corners thereoffrom its proper position with respect to the workpiece detector meanswhereby the sewing machine is inadvertently stopped. This results in asubstantial reduction of operation efficiency.

According to the third method, when a workpiece detector means detectsthe trailing end edge of a workpiece, the sewing machine stops and athread cutter means is operated. However, this method involves thedrawback that when a seam is formed along an end edge of a piece ofcloth having a complicated configuration or of a piece of cloth having asquare configuration such as a neck, collar, sleeve or cuff, each timethe workpiece end edge deviated at a corner of square or concavo-convexconfiguration from its proper position with respect to the workpiecedetector means, the sewing machine stops and the thread cutter means isoperated, thereby making it impossible to form a continuous seam alongthe workpiece end edge and impairing the quality of a sewn product.

DISCLOSURE OF THE INVENTION

The purpose of the present invention is to provide a sewing machinecontrol device which eliminates the drawbacks inherent in the prior art.

According to the present invention, in order to attain this purpose thesewing machine is driven or stopped in response to the operation of thepedal and when a workpiece detector means disposed upstream of thesewing zone in the machine in the workpiece feed direction detects thetrailing end edge of a workpiece, the sewing machine is automaticallystopped independently of the above-mentioned operation of the pedal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front elevational view of the sewing zone in asewing machine embodying the present invention;

FIG. 2 is an explanatory view showing the formation of a seam on aworkpiece W by the embodiment of FIG. 1;

FIG. 3 is a block diagram of the main electrical circuit in theembodiment;

FIG. 4 is a time chart of the electrical circuit of FIG. 3;

FIG. 5 is a diagram of the control circuit of the motor and sewingmachine operation means in the embodiment; and

FIG. 6 is a flow chart for controlling the motor and thread cutter.

BEST MODE FOR CARRYING OUT THE INVENTION

First referring to FIG. 1, there is schematically shown a portion of asewing machine to which the sewing machine control device according tothe present invention is applied.

In FIG. 1, 1 denotes the throat plate, 2 denotes the workpieceholding-down foot which is adapted to be resiliently pressed against thethroat plate 1 and to pinch a workpiece W in cooperation with aworkpiece feed dog (not shown), 3 denotes a needle adapted to moveupwardly and downwardly in response to the rotation of the sewingmachine main shaft (not shown), 4 denotes a reflector plate secured tothe upper surface of the throat plate 1 upstream of the workpieceholding-down foot 2 in the workpiece feed direction and 5 denotes aworkpiece detector means disposed above and spaced apart from the throatplate 1. The workpiece detector means 5 comprises a light emittingportion (not shown) for emitting light to the reflector plate 4 and alight receiving portion (not shown) for receiving the light reflectedfrom the reflector plate to produce an absence-of-workpiece signal whenthe workpiece W is not present between the reflector plate 4 anddetector means 5 and a presence-of-workpiece signal when the detectormeans is shielded from the reflector plate 4 when the workpiece ispresent therebetween. Although not shown, the sewing machine is providedwith a thread cutter means disposed below the throat plate 1 andoperable while the needle 3 is rising from the bottom dead point by theoperation of an operation means such as an electromagnet to arrest andcut upper and lower threads attached to the workpiece W, and a needleposition detector means (NP in FIG. 5) so disposed relative to the mainshaft of the sewing machine that as the main shaft rotates to move theneedle 3 upwardly and downwardly, the needle detector means detects therotational angles of the main shaft corresponding to upper and lowerpositions of the needle 3 respectively, and produces position signalsrepresenting the positions of the needle.

An electrical circuit is provided for controlling the sewing machine andthis electrical circuit is shown in FIG. 3. In FIG. 3, WS denotes adetector circuit incorporated in the light receiving section of theworkpiece detector means 5 and adpated to produce an L level orabsence-of-workpiece signal in its light receiving condition and an Hlevel or presence-of-workpiece signal in its shielded condition, DPdenotes a display circuit including a lamp adapted to be energized whena presence-of-workpiece signal is produced, CT₁, CT₂ denote countercircuits adapted to count up and down edges of signals having arectangular wave form and coming from gate circuits G₁, G₄,respectively, DSW denotes a number-of-nullifying-stitches setting switchset to numeral values in the range of 0-99, for example, to set numbersof stitches which nullify detection signals from the detector circuitWS, and ESW denotes a number-of-stitches-up to-stop setting switchsettable to numeral values in the range of 0-9 and adapted to set thenumber of stitches to be sewn from the time when the end of the seam onthe workpiece W has been detected based on a detection signal from thedetector circuit WS to the time when the sewing machine stops.

CP₁, CP₂ denote comparator circuits adapted to compare a count on thecounter CT₁ with a value set on the switch DSW and a count on thecounter CT₂ with a value set on the switch ESW, respectively, and whencounts on the counters coincide with the respective values set on theassociated switches, the comparator circuits CP₁ and CP₂ producecoincidence signals of H level. CT₃ denotes a counter circuit havingoutputs a and b in which the output a produces an output signal of Llevel while the numeral values of 0-2 are being counted whereas theoutput b produces an output signal of L level while the numeral valuesof 0 and 1 are being counted. TSW denotes a switch adapted to set thethread cutting at the termination of sewing as either valid or null andto produce an output of H level at the time of valid thread cutting. FFdenotes a positive edge type flip-flop adapted to be preset at the timeof power source closing, reset by the up-edge of a signal having arectangular wave form from the gate circuit G₇ and set by the up-edge ofa signal having a rectangular wave form from a pedal switch LSW, anexplanation of which will be made hereinafter.

G₁ -G₈ denote gate circuits and I₁ -I₆ denote inverter circuits. TheNAND gate circuit G₁ remains open while the comparator circuit CP₁ isproducing an anticoincidence signal, allows a lower position signal fromthe needle position detector means NP to pass through the gate circuitG₁ to provide an output of L level which is then input to the counterCT₁ and closes when the comparator circuit CP₁ produces a coincidencesignal. The AND gate G₂ provides an output of H level when the detectorcircuit WS produces an absence-of-workpiece signal and the comparatorcircuit CP₁ produces a coincidence signal, the AND gate opens to allow alower position signal to pass therethrough when the gate G₃ circuit G₂provides an output of H level and the NAND gate circuit G₄ remains opento allow a lower position signal to pass therethrough while thecomparator circuit CP₂ is producing an anticoincidence signal to inputthe signal to the counter CT₂ and closes when the comparator circuit CP₂produces a coincidence signal. The OR gate circuit G₅ produces anintermediate speed setting signal of L level during the time durationfrom the time at which the detector circuit WS produced anabsence-of-workpiece signal (since the gate circuit G₂ has produced anoutput of H level) to the time at which the comparator circuit CP₂produces a coincidence signal. The NAND gate circuit G₆ remains openduring the time duration from the time at which the comparator circuitCP₂ produced a coincidence signal to the time at which the counter CT₃produces an output of H level at its output a to allow an output of thegate circuit G₃ (a lower needle position signal) to pass therethrough tobe input to the counter CT₃. The NAND gate G₇ produces a low speedsetting signal during the time duration from the time at which thecomparator circuit CP₂ produced a coincidence signal to the time atwhich the output a of the counter CT₃ counts "2".

In FIG. 5, M denotes a sewing machine motor operatively connected to themain shaft of the sewing machine and, in the illustrated embodiment, themachine motor is in the form of an electromagnetic clutch motor. NPdenotes the above-mentioned needle position detector means which isadapted to detect rotational angles of the main shaft corresponding toupper and lower positions of the needle to produce upper and lowerposition signals of L level. PS denotes an operation detector meansassociated with the pedal (not shown) of the sewing machine andcomprising a pedal switch LSW adapted to produce an L level signal uponthe actuation or depression of the pedal and an H level signal upon therelease of the pedal and an operation detection section PV adapted toproduce a speed setting signal the value of which varies in proportionto variations in the amount by which the pedal is depressed relative toits fully released position. MD denotes a motor drive circuit adapted todrive and stop the motor M and MC denotes a microcomputer adapted tocontrol the drive circuit MD and also the machine operation means forthe thread cutting operation and the like.

The microcomputer MC controls the motor and thread cutter means inaccordance with the flow chart of FIG. 6.

In operation, it is first of all determined whether the pedal switch LSWis in its ON or OFF condition; when the switch is in its ON condition,the amount by which the pedal is depressed or the value of the signalfrom the detection section PV is read and the drive circuit MD iscommanded to drive the motor at a speed corresponding (in proportion) tothat amount or value. Next, the condition of the pedal switch LSW isagain determined and when it has been determined that the switch is inits OFF condition, a lower position signal is produced to operate the"stop-in-lower position subroutine" for controlling the motor M so as tostop the sewing machine with the needle disposed at its predeterminedlower position. Alternatively, when the pedal switch LSW is in its ONcondition, the output of the gate circuit G₅ is determined and when thegate circuit G₅ produces an intermediate speed setting signal (L level),the drive circuit MD is commanded to drive the motor M at apredetermined intermediate speed. Next, the output of the gate circuitG₇ is determined and when the gate circuit produces a low speed settingsignal (L level), the drive circuit MD is commanded to drive the motor Mat a predetermined low speed (capable of instantly stopping the sewingmachine) and the output of the gate circuit G₇ is again determined. Whenthe output of the gate circuit G₇ rises, the condition of the pedalswitch TSW is determined and when it has been determined that the switchis in its invalidation-of-thread cutting condition (L level), an upperposition signal is produced to operate the "stop-in-upper positionsubroutine" and thus to control the motor M so as to stop the sewingmachine with the needle disposed in its predetermined upper position.When the pedal switch TSW is in its valid (H level) condition, it isdetermined whether a lower position signal is being produced and whetherthe output of the gate circuit G₈ is L level. When both these conditionsare satisfied, a thread cutting command is produced to operate thethread cutter means and thereafter the "stop-in-upper positionsubroutine" is operated.

With the above-mentioned construction and arrangement of the componentsof the sewing machine control device of the present invention, theoperation of the control device will now be described by referring tothe instance in which a seam Y is formed along the side and end edges ofa substantially rectangular workpiece W as shown in FIG. 2. Thenumber-of-invalid-stitches setting switch DSW is set to a numeral valuecorresponding to the number of stitches expected to be sewn from thesewing initiation point P₀ to the point P₃ short of the sewingtermination point P_(e), for example "70", and thenumber-of-stitches-upto-stop setting switch E is set to the numeralvalue corresponding to the number of stitches expected to be sewn fromthe time when the trailing end of the workpiece W has moved to theworkpiece detector means 5 and an absence-of-workpiece signal has beenproduced to the position three stitches short of the sewing terminationpoint P_(e), for example, "6".

Next, when the point P₀ on the workpiece W is disposed in the positionopposite to the needle drop point as shown in the time chart of FIG. 4and the flow chart of FIG. 6, the workpiece detector means 5 (WS)produces a presence-of-workpiece signal (H level) and when the pedal isdepressed, the pedal switch LSW turns on to produce an output of Llevel. The sewing machine motor M is driven at a speed based on thevalue determined by the detection section PV of the operation detectormeans PS which relates to the amount of pressure on the pedal. Thecounter CT₁ has input thereto lower position signals from the needleposition detector means NP which are produced as the main shaft of thesewing machine rotates through the gate circuit G₁ and counts thesignals. When the sewing operation has proceeded to the point P₁ at thefirst corner of the workpiece, since the workpiece detector means 5 ispositioned upstream of the needle drop point in the workpiece feeddirection, the workpiece detector means 5 is positioned at the point B₁outwardly of the workpiece W and an absence-of-workpiece signal isproduced, but since the count of the counter CT₁ does not coincide withthe set value, the comparator circuit CP₁ provides an output of L level,the gate circuit G₂ remains unchanged and accordingly, the output of theworkpiece detector means 5 is nullified. At the point P₁, the pedal isreleased to turn the pedal switch LSW off whereby the sewing machine(motor M) stops with the needle disposed in a lower position inaccordance with the "stop-in-lower position subroutine".

When the pedal is depressed after the workpiece W has been rotated aboutthe needle 3 so that the sewing operation has proceeded to the point P₂at the second corner of the workpiece, the sewing machine is similarlydriven. At the point P₂, the sewing machine is similarly stopped andthereafter, when the pedal is again depressed after the workpiece W hasbeen similarly turned, the sewing machine is driven and the sewingoperation proceeds towards the termination point P_(e).

At the point P₃ between the point P₂ and termination point P_(e), sincethe number of stitches is 70 and the count of the counter CT₁ coincideswith the value set on the setting switch DSW, the comparator circuit CP₁produces a coincidence signal of H level which closes the gate circuitG₁ and opens the gate circuit G₂. When the sewing operation hasproceeded to a position short of the termination point P_(e), thetrailing end of the workpiece W moves from a proper detected positionrelative to the workpiece detector means 5 and an absence-of-workpiecesignal is produced to cause the gate circuit G₂ to provide an output ofH level and open the gate circuit G₃ whereupon the signal is inverted bythe inverter I₅ and input to the gate circuit G₅, and since thecoincidence circuit CP₂ provides a L level output, the gate circuit G₅provides an L level output. Since the L level output of the gate circuitG₅ is an intermediate speed setting signal, the microcomputer MCprovides an intermediate speed command to the drive circuit MD whichdrives the sewing machine (motor M) at an intermediate speed. Since thegate circuit G₃ is open at this time, when a lower position signal isproduced, the gate circuit G₃ provides an H level output which is inputthrough the gate circuit G₄ to the counter CT₂ which then commencescounting. When the counter CT₂ counts the number of six stitches, sincethe count coincides with the setting value of the setting switch ESW,the comparator circuit CP₂ produces a coincidence signal of H levelwhich closes the gate circuit G₄ and is input to the gate circuits G₆,G₇. Since the output a of the counter CT₃ is at H level while thecounter is counting 0-2, the gate circuit G₇ is open and produces an Llevel output (low speed setting signal) in response to a coincidencesignal from the comparator circuit CP₂ and the microcomputer MC providesa low speed command to the drive circuit MD to drive the sewing machine(motor M) at a low speed. And since the gate circuit G₆ opens inresponse to the coincidence signal, the gate cirucit is at L level whena lower position signal is produced and the counter CT₃ commencescounting. When the counter CT₃ counts a lower position signal of thecount of two stitches, the output b of the counter is at H level. Whenthe switch TSW is set for effective thread cutting, the gate circuit G₈produces an L level output (thread cutting signal) and the thread cutteroperation means operates upon the generation of a next lower positionsignal and the "stop-in-upper position subroutine" operates. Threadcutting is carried out while the needle 3 is rising and the sewingmachine stops with the needle disposed in an upper position. When thecounter CT₃ counts lower position signals, since the output a of thecounter is at L level, the output of the gate circuit G₇ is at H levelto reset the flip-flop FF to make the terminal Q of the flip-flop FF Hlevel and reset the counters CT₁, CT₂ and CT₃ and nullifies the ONoutput of the pedal switch LSW with the pedal held in its depressedcondition.

In the above-mentioned embodiment, although the workpiece detector meansis shown as being photosensitive, the detector means may be of a typewhich is not photosensitive.

According to the present invention, there are provided an operationcircuit which drives the motor in response to an actuation signal andstops the motor in response to change from a presence-of-workpiecesignal to an absence-of-workpiece signal or a stop signal, a digitalcount circuit which produces an operation signal when a certain numberof position signals has been counted which corresponds to the number ofstitches sewn upto a position short of the sewing termination end edgeof the workpiece, and a regulator circuit which interrupts at a pointbetween the workpiece detector means and the operation circuit duringthe time duration from the moment at which an actuation signal isproduced to the moment at which an operation signal is produced. Thus,even when the workpiece deviates from the workpiece detector means atits trailing end where the sewing operation terminates, the sewingmachine will not stop inadvertently and the thread cutter means will notoperate inadvertently either. Therefore, even when seams are formedalong an end edge having a complicated configuration, the operator canperform the sewing operation safely by suitable control of the pedal tothereby improve operation efficiency. Furthermore, since the sewingmachine will not stop inadvertently nor the thread cutter means operateinadvertently, the present invention exhibits the practical advantagethat the quality of a sewn product can be improved by forming acontinuous seam along end edges of a workpiece.

We claim:
 1. An apparatus for use in sewing a workpiece, said apparatus comprising means for reciprocating a needle to stitch the workpiece in a sewing zone, said means including a motor which is operable at any one of a plurality of speeds to effect reciprocation of the needle at any one of a plurality of speeds and means for effecting relative movement between the workpiece and needle to move the sewing zone relative to the workpiece as the workpiece is stitched, first circuit means for counting a first predetermined number of stitches and providing a control signal in response to the counting of the first predetermined number of stitches, detector circuit means for providing a control signal in response to movement of the sewing zone to within a predetermined distance of an edge portion of the workpiece, and control means connected with said motor, first circuit means and detector circuit means for reducing the speed of operation of said motor from a relatively high speed to an intermediate speed in response to a control signal from said detector circuit means after a control signal has been provided by said first circuit means, said control means including means for rendering said control means ineffective to reduce the speed of operation of said motor to the intermediate speed in response to a control signal from said detector circuit means prior to the counting of the first predetermined number of stitches by said first circuit means to prevent said control means from reducing the speed of operation of said motor in response to the detection of an edge portion of the workpiece by said detector circuit means prior to the stitching of the first predetermined number of stitches, second circuit means for counting a second predetermined number of stitches and providing a control signal in response to the counting of the second predetermined number of stitches, said control means including means for initiating the counting of the second predetermined number of stitches simultaneously with the reduction in the speed of operation of said motor to the intermediate speed and means for reducing the speed of operation of said motor from the intermediate speed to a lower speed in response to a control signal from said second circuit means, and third circuit means for counting a third predetermined number of stitches, said control means including means for initiating the counting of the third predetermined number of stitches simultaneously with the reduction in the speed of operation of said motor to the lower speed and means for initiating a control function in response to the counting of the third predetermined number of stitches.
 2. An apparatus for use in sewing a workpiece, said apparatus comprising means for reciprocating a needle to stitch the workpiece in a sewing zone, said means including a motor which is operable at anyone of a plurality of speeds to effect reciprocation of the needle at anyone of a plurality of speeds and means for effecting relative movement between the workpiece and needle to move the sewing zone relative to the workpiece as the workpiece is stitched, first circuit means for counting a first predetermined number of stitches and providing a control signal in response to the counting of the first predetermined number of stitches, detector circuit means for providing a control signal in response to movement of the sewing zone to within a predetermined distance of an edge portion of the workpiece, and control means connected with said motor, first circuit means and detector circuit means for reducing the speed of operation of said motor from a relatively high speed to an intermediate speed in response to a control signal from said detector circuit means after a control signal has been provided by said first circuit means, said control means including means for rendering said control means ineffective to reduce the speed of operation of said motor to the intermediate speed in response to a control signal from said detector circuit means prior to the counting of the first predetermined number of stitches by said first circuit means to prevent said control means from reducing the speed of operation of said motor in response to the detection of an edge portion of the workpiece by said detector circuit means prior to the stitching of the first predetermined number of stitches, second circuit means for counting a second predetermined number of stitches and providing a control signal in response to the counting of the second predetermined number of stitches, said control means including means for initiating the counting of the second predetermined number of stitches simultaneously with the reduction in the speed of operation of said motor to the intermediate speed and means for reducing the speed of operation of said motor from the intermediate speed to a lower speed in response to a control signal from said second circuit means, and third circuit means for counting a third predetermined number of stitches and providing a control signal in response to the counting of the third predetermined number of stitches, said control means including means for initiating counting of the third predetermined number of stitches simultaneously with the reduction in the speed of operation of said motor to the low speed and means for initiating the cutting of a thread connected with the needle in response to a control signal from said third circuit means.
 3. A sewing machine control device comprising:a motor (M) operatively connected to the main shaft of a sewing machine for driving and stopping said main shaft; operation means (LSW) adapted to cause said motor to produce an actuation signal during the actuation of said sewing machine and a stop signal during the stopping of said sewing machine; needle position detector means (NP) operatively connected to said operation means and adapted to produce a position signal by detecting a particular rotational angle of said sewing machine main shaft; workpiece detector means (5, WS) operatively connected to said needle position detector means in opposition to a workpiece movement path in a position upstream of the sewing zone of said sewing machine in the workpiece feed direction and adapted to produce an absence-of-workpiece signal by detecting the absence of a workpiece; and an electrical circuit operatively connected to said workpiece detector means, said electrical circuit having: an operation circuit adapted to drive said motor in response to an actuation signal and stop said motor in response to an absence-of-workpiece signal; a digital count circuit adapted to produce an operation signal when the number of position signals which has been counted corresponds to the number of stitches sewn up to a position short of the sewing termination edge of said workpiece; and a regulator circuit adapted to interrrupt operation of said motor during the time duration from the moment when said actuation signal is produced to the moment when said operation signal is produced; said regulator circuit including means for counting a predetermined number of stitches, means for initiating the counting of the predetermined number of stitches simultaneously with a reduction in the speed of operation of said motor to a lower speed and means for initiating a control function in response to the counting of the predetermined number of stitches. 